In recent years, immunoregulating therapy has come to be practiced to cure such autoimmune diseases as rheumatoid arthritis, generalized lupus erythematodes, etc. or malignant tumor and a variety of drugs have been developed. As an example of such drugs, the application of levamisole, which is a levorotatory isomer of tetramisole, to the drugs for immunotherapy of cancer and such autoimmune diseases as rheumatoid arthritis has due attention.
Though it has been reported that levamisole has efficacy in said diseases to a certain degree, it has no singularity in its efficacy and does not always display its efficacy satisfactorily either. Many immunoregulating drugs have been developed but most of them not only lack singularity in their remedial activities but also raise a problem of side effects, and no satisfactory drugs of this kind are available as yet.
Meanwhile, it is mentioned in the "Journal of American Chemical Society" vol. 64, pp. 2709-2712, 1942, that a derivative of barbituric acid is obtained from 2-aminothiazoline and diethyl malonate, and that this compound has a hypnotic action and an anesthetic action as well; however, nothing is mentioned in the journal as to other efficacy besides its hypnotic and anesthetic actions.
The inventors of the present invention have prepared a novel thiazolo[3,2-a]pyrimidine derivative which is a novel barbituric acid derivative different from the derivative of barbituric acid mentioned in the above journal and made a focused study of the efficacy of this newly prepared compound. The result is a remarkable finding that it is a compound which has a specific immunoregulating action different from an action owned by levamisole, or the immunoregulating action based on a pharmacological action apart from hypnotic and anesthetic actions, and that, because of its low toxicity, the abovementioned thiazolo[3,2-a]pyrimidine derivative is very useful for curing such autoimmune diseases as rheumatoid arthritis, nephritis, etc., thus producing the present invention.